In the production of cigarettes, a tobacco filler stream is formed from a broad relatively thin stream of tobacco particles and, after trimming, the filler rod is wrapped in paper to provide a continuous cigarette rod from which individual cigarettes are cut. The tobacco particles which are used to provide the broad stream of tobacco preferably have a narrow range of particle sizes and, in particular, the presence of stem or other heavy debris is usually avoided.
There are two conventional methods of forming the filler stream. In one of these methods, the broad relatively thin stream of tobacco particles is conveyed in a rapidly-moving upwardly-flowing air stream in a confined chute for of narrow depth for collection on a transversely-moving foraminous conveyor. In the other of the methods, the particles in the broad stream are allowed to fall from the end of a feed belt under the influence of gravity onto a transversely-moving conveyor.
In the former method, the tobacco particles are accelerated in the upwardly-moving air stream to result in substantially complete separation of the tobacco particles in the air stream, allowing the formation of a filler stream of substantial uniformity from the separated particles. In contrast, in the latter method, complete separation of the tobacco particles is not ensured and lumps of tobacco often are present in the downwardly-moving stream, resulting in a less uniform filler stream.
The former method, however, suffers from the drawback that the narrow chute, necessary to achieve the velocity of air flow therethrough, is sensitive to differences in air flow, leading to problems of chute or "chimney" choking, due to accumulation of tobacco particles therein, thereby necessitating machine shutdown.
In accordance with one aspect of the invention, the formation of a filler stream from a downwardly-moving broad stream of tobacco particles is considerably improved by providing accelerated substantially completely separated tobacco particles in the broad stream, so that the uniformity of the filler stream is at least comparable to that of the cigarette maker using the upwardly-flowing stream of tobacco particles, while the potential problem of chute choking is eliminated and the prior art use of feed belts is avoided.
The tobacco which is fed to the feed mechanism used to produce the broad stream of tobacco consists of cut leaf which contains not only the desired tobacco particles but also some undesirable heavy stem and debris. It is common practice to include some form of winnowing technique to separate the usable tobacco particles from the remainder thereof prior to formation of the broad stream.
In U.S. Pat. No. 3,030,965, which describes the formation of the filler stream from upwardly-moving discrete tobacco particles conveyed by a rapidly-moving air stream confined within a chute by catching the tobacco particles on a foraminous conveyor, the winnowing technique involves picking the tobacco particles at a high rate of speed from a carding drum and passing the particles in a separated condition at a high rate of speed in a direction generally transverse the direction of movement of the broad curtain. Through a confined enclosed area.
The particles desired to form the broad stream are subjected to a centripetal force to cause them to change direction and enter the chute. Those heavy particles whose momentum is too large to be affected significantly by the centripetal force, consisting of stem and other heavy debris, continue in the same path and do not enter the chute.
Air flow is used to apply the centripetal force to the usable particles to cause them to abruptly change their direction to enter the chute wherein they are accelerated by the air flow therethrough to increase their separation one from another, the particles assuming a free flight path from the original direction of movement into the chute by virtue of the air flow across the picked particles into the chute.
The winnowing operation in this prior patent takes place in an enclosed area which confines the stream of picked particles into a narrow passage. The presence of the heavy stem and debris in the stream of picked particles may cause choking of this narrow passage, with consequential machine shut-down.
In accordance with a second aspect of the invention, there is provided a winnowing method for the formation of a vertically-moving broad stream of tobacco particles using air flow which avoids the prior art problems associated with confined areas and the necessity for substantial changes in direction.
A particularly preferred aspect of the invention provides a method for simultaneously winnowing and accelerating tobacco particles for formation of a downwardly-moving broad stream of tobacco particles from which a filler stream may be formed.